Electron tube



@itenteol Jan. 4, 1938 PATENT OFFICE ELECTRON TUBE Ioury G. Malofi,Philadelphia, Pa., assignor to Radio Corporation of America, a.corporation or" fielaware Appiication March 21,

10 Claims.

This invention relates to electronic devices, and principally toelectronic devices of the cathode ray type which are frequently referredto as Braun tubes. Such types of electronic devices are 5 of greatimportance in connection with television systems both at the receiverand transmitter and find considerable use also as oscillographs andOscilloscopes. Other and varied uses of this general type of electronicdevice are, of course, obvious and need no explanation.

The cathode ray tube of the prior art usually .used for television andoscilloscope purposes employs a translucent screen which has theproperty of fluorescing when subjected to the bom- 15 bardment of anelectronic beam. In cases where it is desired to produce variations inintensities of the resulting fluorescent effects, which variations mightbe in accordance with variations in photoelectric currents resulting ata point of transmisgo sion in accordance with the scanning of a subjectof which the electro-optical image is desired, the cathode ray beam orpencil of electrons may be modulated by means of an electrostaticcontrol electrode or grid which is disposed in the path of the electronsmoving from the cathode, as the electron source, toward the fluorescentviewing plane. To produce this intensityvariation the control electrodeor grid is biased under the influence of the applied signal effects andthereby varies the degree of fluorescence in accordance with the controlexercised upon the developed cathode ray.

According to still other arrangements of the prior art, proposals aremade for controlling the intensities of the observable effects upon thefluorescent end wall of the cathode ray tube by deflecting under controlof the applied signals the cathode ray pencil with respect to anaperture or opening in a screen plate or with respect to a limiting orbeam deflning'edge of a screen plate which is opaque to the'passage ofthe electrons. This type of prior art arrangement functions so as tocontrol variably the number of electrons which pass through the openingor past the beam defining edge of the shield.

Still other arrangements of the prior art have provided for intensitycontrol of the fluorescent effects by a variation in the velocity ofimpact of the electron stream upon the fluorescent screen. Otherarrangements operate to control the observable intensity of thefluorescent spot by varying the velocity of traversal of the cathode raystream projected at constant instantaneous impact velocity upon thefluorescent viewing plane so that the variations produced in the periodsof 1934, Serial No. 716,684

actual impact of the cathode ray beam at any differential area upon thescreen produce the effects of varying lights and shadows from theresulting light spot, the intensity of fluorescence being a function ofboth velocity of impact and time of impact.

All such arrangements of the prior art while, in general, satisfactory,particular reference being. made to the grid control eiTect souniversally used, nevertheless are somewhat unsatisfactory for extremelyaccurate control for one reason or another. One of the more importantobjections of these systems of the prior art, which this inventionattempts to obviate, is that the intensity controls of the types aboveoutlined frequently cause the eflects of streaking or the like in theviewed electrooptical effects produced from screen fluorescence.

While the grid control has, up to the present time, been practicallyuniversally adapted, it nevertheless has an inherent disadvantage inthat upon impressing various voltages or biasing potentials to producethe control action a change or variance in the cross-sectional area ofthe electron beam takes place. This effect, as will become more apparentfrom what follows, results in streakiness of the fluorescent image andis what this invention attempts to overcome.

Cathode ray tube, as designed for television work, reference being madeherein to the subject of television merely in order to illustrate onesuitable use for a type of cathode ray tube and control therefor, asherein disclosed, are usually characterized by a long tubular neck, oneend of which carries the base of the tube, and a conical portionterminating in a section whose normal projection is perpendicular to theaxis of the tube. This section is usually concave on the inside, although for small tubes especially it may be flat or even convex, andprovided with screen structure of a fluorescent character upon which thecathode ray stream or pencil developed in the neck portion of the tubeimpinges. This pencil or beam of rapidly moving electrons, termed thecathode ray, has its origin in a heated cathode or, where desired, evena cold cathode located at the base end of the tube. From the point oforigin of the cathode ray beam or pencil to the point where it strikesthe fluorescent screen the beam is controlled by either electrostatic orelectromagnetic fields or both so arranged as to accelerate, focus anddeflect the cathode ray pencil in the direction or directions desired.

One suitable means for deflecting the cathode ray beam is by the use ofelectrostatic deflecting f plates conveniently located in the neck ofthe tube, or, where desired, externally of the tube. An electrostaticfield produced between these plates upon the application of voltages ofsuitable frequency thereto produces an acceleration of the beam in linewith the field between the plates.

For television work two sets of deflecting plates may be used and, ifso, the surfaces of each set are at right angles toeach other. Such anarrangement permits deflection of the cathode ray pencil in two planesperpendicular to each other but both normal to the axis of the tube.Where desired, of course, it is possible to substitute electromagneticdeflection for the electrostatic deflection hereinabove suggested and ithas been found in many instances that most satisfactory results areobtained by combining electromagnetic and electrostatic deflectionsystems, in which case the electrostatic deflecting plates are formed ofnon-magnetic material and supported beneath the magnetic deflectingcoils. In this last suggested embodiment substantially no interactingfields exist to produce distortion,

To control the intensity of the cathode ray thus deflected andpositioned upon the tube screen, according to the prior art as abovementioned, the electrostatic or grid control usually consisted of anelectrode member substantially surrounding the electron emitting area insuch manner that the issuing electrons were drawn through an aperture ofpredetermined size, but of substantially less area than the emittingarea. Modulation of the cathode ray beam to vary the intensity of theresulting fluorescent effects was accomplished by varying the negativebias upon the control electrode or grid member. With zero bias on thegrid electrode the effective aperture has been found to be the same asthe actual aperture. However, as the negative bias is increased theeffective diameter of the aperture in the control grid member, ineffect, decreases in size with the result that the size of the beam spoton the screen also decreases in diameter. In television scanning thiswill result in a Variation in the light spot diameter with each changein modulation. This effect then becomes observable in the form of darklines on the fluorescent screen because the line definition at all timesthroughout the scanning period remains constant.

It is, therefore, one of the primary objects of this invention toovercome this changing spot size defect and to produce a scanned area onthe fluorescent viewing screen which is devoid of all streaked effects.

Still other objects of the invention are to provide more suitable meansfor controlling the density of a beam of electrons.

Another object of the invention is to provide means by which a beam ofelectrons may be modulated and controlled by suitable controllingelectrodes without many way affecting the operation or changingthe'actual diameter of the resulting area of fluorescence upon theviewing screen.

Other objects 'of the invention are to provarying the intensity of acathode ray pencil of electrons in which the control is more sensitivethan that found in arrangements heretofore used in the prior art; toprovide a control systemwhich is extremely simple in its arrangement; toprovide a control system which readily adapts itself to provide acontrol system that is extremely efficient in its operation.

Still other and further objects of the invention will become apparentand suggest themselves to those skilled in the art to which theinvention relater from reading the following specification and claims inconnection with the accompanying drawing, wherein:

Fig. 1 illustrates one type of cathode ray tube to which this inventionis applicable;

Fig. 2 illustrates one form of electrode structure which may be enclosedwithin the tube shown by Fig. 1;

Fig. 20!. represents a transverse section through the electron stream onthe line AA;

Fig. 3 shows various forms of modulating electrode which may beincorporated as a part of the electrode structure within the tube ofFig. 1;

Fig. 3a designates an electrode structure having a circular apertureacross which the control element is provided i Fig. 31) indicates 'anelectrode structure with a square aperture controlled similarly to thearrangemen't of Fig. 3a.; and

Figs. 3c and 311 respectively indicate longitudinal sections of theelectrode structures shown by Figs. 3a and 3b.

The general type of cathode ray tube used for television purposes issimilar to that shown by Fig. 1. This tube, as has been above stated, ischaracterized by a long tubular neck portion 1 upon one end of which issupported the base 2. The other end of the tube is a conical portion 3.On the inner end of the conical tube portion 3 a fluorescent screen 4 issupported. The cathode rays are generated within an electron gunstructure designated as 5 and the rays or electron stream thus developedand projected toward the fluorescent screen member 4 may be suitablydeflected in one direction by applying suitable con trolling voltages tothe electrostatic deflecting plates 6 and then the beam may be deflectedin a direction at right angles to the first plane of deflection by meansof a pair of electromagnetic deflecting coils I supported adjacent theplates 5. Of course, magnetic deflection in two directions orelectrostatic deflection in two directions may be provided wheredesired. Whenever a combination of electro-magnetic and electrostaticdeflection is used the electrostatic deflecting members are preferablyformed from nonmagnetic material so as not to be subjected to theinfluence of the magnetic deflecting fields.

According to the conventional type of cathode ray tube design a controlgrid member, such as the structure I0 shown by Figs. 3a and 3c, isusually arranged to surround substantially the cathode emitting surfaceand the developed electrons are projected toward the fluorescent screenstructure 4 through the aperture II which may be of the size of theemitting-area, or preferably larger than the emitting area in order thatall emitted electrons may pass through. Such structure as is used in thecathode ray tubes now usually known varies the modulation of the beam orelectron stream by varying the negative bias applied to the grid orcontrol electrode H). For conditions of zero bias on this controlelement IO the effective aperture through which the oathode ray stream15 is adapted to pass is the same as the actual aperture H sothatthecathode ray pencil emerging from thegrid structure will have anactual electronic diameter equal to the diameterof the aperture II.However, as the negative bias is increased to vary the intensity of theresulting electronic light spot on the fluorescent screen structuretheeffective diameter of the aperture II decreases due, for example, torepulsion of the emerging electrons from the edges of the diaphragmmember, so that the spot size also decreases. This efiect produces, ashas been above defined in the statement of invention, dark lines on thefluorescent screen because the line definition remains always constant.

According to the present invention these above mentioned difiicultieshave been substantially overcome by changing the control electrodestructure to some extent from the form now used in tubes known in theart. In the new form of the control electrode herein disclosed thecontrol electrode structure includes the disk or plate member ID formedwith the shielding structure I2 attached thereto so that it resemblesclosely the usual grid structure I ll above discussed but isdistinguishable therefrom both in formation and operation as will hereinbe pointed out. As shown by all of Figs. 3a through 3d inclusive, theaperture of the control electrode It may be round, as shown by theapertures H of Figs. 3a and 30, or square, as shown by the aperture I3of Figs. 3b and 301, or may be of any other suitable formation, such astriangular, rhomboidal, rectangular or of a most irregular shaping whereit is desired to produce peculiarly shaped light spots on the screen 4.In addition, the aperture should be formed slightly larger than theaperture in the regularly used control elements, wherein the light spotdiameter depended upon the aperture diameter, and as above mentionedequal or exceed the area of emission of the electrons. Across theaperture H or H) in such manner as to divide the area of the apertureinto two substantially equal parts there is attached to either sidethereof, by welding or by other suitable means, a Wire M which isstretched and forms electrical contact with the disk surface it. Theeffect of this design, as can be seen more particularly from Fig. 2 ofthe drawing and also from Fig. 2a thereof, is to control the center ofthe electron pencil or beam I5, which is developed by drawing theelectrons issuing from the electron emitting surface I! of the heatedcathode member I8 by means of the application of suitable positivevoltages upon an anode electrode is for example, rather than tochangethe beam diameter as is the case when modulation is produced by theusualtype of control electrode. The apertures II and I3, depending uponthe shaping of the disk member as in Figs. 3a and 3c, are so large thatlittle or no current will be cutoff from the outside of the electronbeam and the wire I 4 stretched across the aperture will cut a diametricswath from the beam l5. As the bias on the control electrode comprisingthe disk member Ill and the shielding portion I2 is increased negativelythe apparent size of the wire M as regards the control of the electronbeam will increase. This effective or apparent increase in the size ofthe wire [4 causes a reduction in the number of electrons forming thecentral portion of the electron beam or pencil it which passes throughthe aperture 20 of the disk member 2| forming a part of the anodestructure l9. This effect, in turn, results in an electron stream whichtakes the general form of the aperture 29 of the electrode l9 exceptthat the fluorescent spot produced upon the fluorescent screen structure4 is divided by the wire member l4 into two parts as can be readilyappreciated from an observation of Fig. 2a which represents acrosssection through the electron stream on the line AA intermediate theaperture 20 and the screen structure 4. From what has been above stated,it will be appreciated that the wire Hi effectively casts its shadowupon the screen structure 5 but this shadow is not in any waydetrimental to any detail of the area scanned provided that the electronbeam is swept back and forth across the fluorescent screen structure insuch manner that the resulting shadow or dark line produced isperpendicular to the direction of beam motion, for example, if theplates 6 produce rapid beam motion across the screen 4 then the area ofthe beam in which the electrons are controlled will be perpendicular tothe path of the deflected beam.

The foregoing description is intended to illustrate but a single broadform of the invention and to set forth broadly a new principle ofcontrolling an electron stream. Therefore, it is believed to be obviousthat I may without departing from the spirit and scope of this inventionprovide other and various ways and means for controlling the intensityof the fluorescent spot resulting upon the fluorescent screen of acathode ray tube or other type of electronic device as long as theeffect of variation in the size or diameter of the resulting fluorescentspot is avoided. I, therefore, believe myself, in accordance with themodifications of this general scheme herein suggested, to be entitled tomake and use any and all of these modifications which fall fairly withinthe spirit and scope of the invention as set forth by the appendedclaims.

Having thus described the invention, what I claim and. desire to secureby Lettters Patent is the following:

An electron tube comprising a source of cathode rays, 2. fluorescentscreen upon which the cathode rays impinge to produce "luminous effects,an apertured shield electrode interposed between the source of electronsand the screen to control the bounding area of the electron beam in itspath from the source to the screen, a control element connected with theshield electrode and dividing the aperture in the shield electrode intotwo substantially equal portions, said control element being adapted toreceive varying voltage to vary the electron density within the centralsection of the electron beam to control thereby the intensity of theluminous effect produced.

2. A cathode ray tube having means for controlling the intensity ofluminous eifects produced by the bombardment of a fluorescent screen ofa cathode ray tube by an electron pencil generated therein whichcomprises a shielding electrode interposed between the source ofelectrons and the screen, said electrode having an aperture therein of across-sectional shaping corresponding to the shaping of the area offluorescence desired through which the electrons pass toward the screen,a wire member stretched across the aperture in the shield member so asto divide the aperture into substantially equal portions, and means forapplying to the shield and wire members varying voltages to cause arepulsion of the electrons in the area adjacent the wire member so as tovary thereby the electron density within the central portion of theelectron pencil and thereby vary the overall intensity of thefluorescent effect resulting while maintaining constant the boundinglimits over which fluorescence takes place.

3, An electron tube for varying the intensity of fluorescent effectsproduced on the fluorescent end wall of a cathode ray tube whichcomprises an electron source, means for causing the electrons generatedat the source to pass toward the fluorescent end wall of the tube as apencil of electrons, means for causing the electron pencil developedwithin the tube to traverse the fiuorescent end wall along a series ofpaths substantially at right angles to each other, a shield elec trodeinterposed between the source of electrons and the fluorescent end wall,said shield having an aperture therein through which the electrons pass,and a conductor stretched across said aperture and in electrical contactwith the shield, said conductor being arranged across the aperture in aplane transverse to the path of rapid motion of the electron pencilacross the fluorescent screen and adapted to divide the aperture intotwo substantially equal portions so that upon the application of signalvoltages to the said conductor the electron density of the electron beamwithin a central portion thereof varies proportionally to the voltageupon the conductor.

4. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the stream and adapted to luminesceunder impact of the electrons, means to focus the emitted electronstream on the target, means to establish a predetermined maximumboundary area of the electron stream impinging upon the target, andmeans acting only within maximum boundary'of the emitted electron streamto vary the area of electron impact Within the maximum boundary area.

5. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the stream and adapted to luminesceunder impact of the electrons, means to focus the emitted electronstream on the target, means to establish a predetermined maximumboundary area of the electron stream impinging upon the target, andmeans acting within the electron stream emitted for bi-secting' theelectron'stream under the control of signals.

6. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the stream and adapted to luminesceunder the impact of the electrons, means to focus the emitted electronstream on the target, means to establish a predetermined maximumboundary area of the electron stream impinging upon the target, andmeans acting within the electron stream for dividing the electron streaminto a plurality of similar segments.

7. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the path of the electron stream andadapted to luminesce under the impact of the electrons, means to directthe emitted electron stream on the target, means to establish apredetermined maximum boundary area of the electron stream directed uponthe target, and means acting within the electron stream for dividing theelectronstream into a plurality of similar segments each of a sizevariable in accordance with the potential of the electron streamdividing means relative to the electron emitting surface.

8. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the stream and adapted to luminesceunder impact of the electrons, means to focus the emitted electronstream on the target, means to establish a predetermined maximumboundary area of the electron stream impinging upon the target, meansacting only within maximum boundary of the emitted electron stream tovary the area of electron impact within the maximum boundary area, andmeans for moving the impact area across the target.

9. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the stream and adapted to luminesceunder impact of the electrons, means to direct the emitted electronstream on the target, means to confine the electrons within apredetermined maximum boundary area of the electrons upon the target, acontrol electrode acting within the boundary limits of the producedelectron stream emitted from the surface for bi-secting the electronstream under the control of signals.

10. A cathode ray tube comprising a surface for emitting a stream ofelectrons, a target positioned in the path of the electron stream andadapted to luminesce under the impact of the electrons, means to focusthe emitted electron stream on the target, means to establish apredetermined maximum boundary area of the electrons upon the target,and control electrode means bi-secting the area of the emitted electronstream and acting only within the electron stream fordividing theelectron stream into a plurality of similar segments each of a sizevariable in accordance with the potential acting upon the controlelectrode means relative'to the electron emitting surface.

IOURY G. MALOFF.

